Silicone sealing compounds which can be cross-linked by the moisture in the atmosphere generally consist of .alpha.,.omega.-dihydroxypolydiorganosiloxanes and silicone oils optionally mixed with precipitated or pyrogenic silicas, powdered quartz, diatomaceous earth, dolomite powder, chalk, zinc oxide and other fillers. When organic silicon compounds containing more than two reactive groups and capable of reacting both with silanol groups and with water are added to such systems (the said reactions generally being accelerated by catalysts such as titanic acid esters and heavy metal salts) and all access to moisture is excluded, then the products obtained are stable in storage and undergo cross-linking to silicone elastomers only when exposed to the moisture in the atmosphere.
Such RTV-1K systems may be used as joint sealants, as already mentioned. The so called neutral system based on carboxylic acid amido alkyl alkoxysilanes as described e.g. in DE-PS 1 247 646 and in DE-PS 1 258 08has proved to be particularly satisfactory but these sealing compounds cannot be coated with lacquers as is frequently necessary in the building industry.
Systems based on carboxylate silanes which can be painted are described in US-PS 3 957 714 and US-PS 4 293 616, the systems described in the first mentioned specification being prepared from needle shaped calcium carbonate with the addition of solvent and those described in the second specification being prepared from coated and ground chalks with the addition of polyethers. The elastomers obtained, however, are greatly altered in their mechanical properties, i.e. they have a high modulus of elasticity, high shore A hardness and low elongation at break, and they undergo volumetric shrinkage and are limited in their capacity to take coats of lacquer. The latter also applies to the systems according to EP 43 501, which can easily be brush coated with paint one to three days after application of the sealing compound but if paint is to be applied at a later date the surface of the sealing compound must first be cleaned with solvents.